BREAKDOWN OF FOURIER LAW NEAR THE SUPERFLUID TRANSITION IN HE-4

The behavior of the superfluid-normal fluid interface in He-4 has been studied in the presence of a heat flux, (Q) over right arrow, in the range 0.1 < Q < 6 erg s(-1) cm(-2). Fourier's Law, (Q) over right arro w = -kappa del T, has been observed, for the first time, to break down very close to the interface. In the nonlinear region, kappa depends o n Q. Theoretical predictions, which do not take gravity into account, are compared with these experimental results. The predicted extent of the nonlinear region agrees well with the data; however, at lower Q, a systematic discrepancy is found that may be ascribed to the effect of gravity on the interface.